Reinforced support sheet and method for making same

ABSTRACT

A reinforced support sheet or plate, especially for making flat gaskets or heat dampening plates is made of a sheet or plate-like support material which is covered with a vulcanizable soft material layer which contains a fiber-like and, if need be, powder-like binder material. The support material is smooth and the soft layer material is composed predominantly of a powder-like, asbestos-free mineral base material. The mineral base material may include mostly a chemically and thermally untreated material and also a chemically and thermally or only thermally treated material. A method for making such a sheet or plate is also disclosed.

This is a continuation-in-part application of co-pending applicationSer. No. 415,812, filed Sept. 8, 1982, now U.S. Pat. No. 4,478,887.

The present invention relates to a reinforced support sheet or plate,especially suitable for making flat gaskets, as well as heat dampeningplates. More particularly, it relates to such a sheet or plate having asheet or plate-like support material which is covered with avulcanizable, soft material which contains fiber-like and, if need be,powder-like base material, as well as a binder material.

A reinforced support sheet of the aforementioned type is disclosed inGerman Auslegeschrift (DE-AS) No. 21 46 309. The subject matter of theaforementioned reference is, in particular, a method for making such areinforced support material. Therein, a dough-like, fiber-reinforcedelastomer mixture (as the soft material) is applied by means of calenderrollers, with the aid of additional water, onto a metallic supportmaterial. The additional water is required so as to avoid an adhering ofthe dough-like material onto the calender rollers. The dough-like softmaterial consists of a rubber-asbestos mixture in a ratio of about 1:1.

As previously indicated, reinforced sheets of the aforementioned typemay be used as a base material for making flat gaskets which aresubjected to high mechanical and thermal stresses, for example, cylinderhead gaskets in combustion engines. In such sealing systems, which aresubjected to high dynamic stresses, the following characteristics of thegaskets employed are important:

(a) adaptability;

(b) pressure resistance;

(c) spring back resilience;

(d) gas and liquid tightness;

(e) temperature resistance;

(f) longitudinal and transverse stability;

(g) hardness of the cutting edges; and

(h) corrosion resistance.

In this respect, the reinforced support sheets or the flat gaskets madeout of these sheets in accordance with the known method of DE-AS No. 2146 309 have substantial disadvantages. The required dough-like basecondition of the soft material requires a high rubber content of thesame. On account of this requirement, gasket plates made from thisreinforced support sheet have a very low pressure resistance, aninsufficient temperature resistancy, as well as a completelyinsufficient longitudinal and transverse stability.

Furthermore, the dough-like mass of the soft material adheres to thecalender rollers during manufacturing. As mentioned above, it has beenattempted to overcome this disadvantage by adding additional water.However, this results in a different significant disadvantage in thatthe adherence ability of the dough-like soft material onto the supportmaterial is severely diminished, especially when a sheet metal is usedwithout a mechanical clamping, fastening or mounting associatedtherewith. It is quite obvious that such a soft material is not usablefor making flat gaskets which have to have the aforementioned criteria.

It is therefore an object of the present invention to afford areinforced support sheet or plate of the aforementioned type wherein thementioned disadvantages of the known reinforced sheets or plates or theproducts made therefrom, for example, gaskets, are eliminated and, inaddition, to provide a simple and cost saving method for making such areinforced sheet or plate.

In accordance with the invention, certain of the foregoing and relatedobjects are obtained by the provision of a support sheet or plate of theaforementioned type, wherein the support material is smooth and the softmaterial layer predominantly consists of a powder-like, asbestos-free,mineral base material. Advantageously, the mineral base material iscomprised mostly of a chemically and thermally untreated material andalso a chemically and thermally or only thermally treated material.

In the inventive reinforced support sheet or plate, a dough-like basecondition of the soft material is eliminated. Thereby, it isadvantageously possible to reduce the rubber content (binder content),thus obtaining a high pressure resistance of the sheet or the flatgaskets made therefrom. A further significant advantage of the inventionis that an application of additional water onto the calender rollers isno longer required. This results in the advantage that an excellentadherence ability of the soft material rolled onto the support materialis obtained, even if the support material is a smooth sheet metal, foil,fleece or fabric. On account of the invention, it is possible toeliminate a mechanical mounting. Consequently, a very great advantagecan be seen in that the reinforced support sheet or plate and theproducts made therefrom, like flat gaskets, for example, cylinder headgaskets, can be made substantially thinner than known gasket sheets orflat gaskets.

In accordance with the invention, certain of the foregoing and relatedobjects are also attained in a method for making such a reinforcedsupport sheet or plate, where the soft material is applied successivelyonto both sides of the support material by means of calender rollersand, afterwards, is dried and vulcanized in an oven. In accordance withthis novel method, a separate pair of calender rollers is provided foreach of the sides of the support material to be coated and this softmaterial is applied as a flowable bulk material onto the given side ofthe support material immediately before it enters the opening betweenthe given pair of calender rollers. The two rollers of the given pair ofcalender rollers are driven at unequal circumferential speeds.

Due to the unequal circumferential speed of the two rollers of the givenpair of calender rollers, a friction is exerted on the flowable softmaterial which is applied onto the support material which results in anexcellent adherence of the soft material onto the surface of the supportmaterial. Due to the different circumferential speeds of the calenderrollers, a further advantage is obtained in that an application ofadditional water on the calender rollers is no longer required. Theelimination of the additional water again enhances the aforementionedadherence ability of the soft material which is rolled onto the supportmaterial. A further advantage of the inventive method is that anadditional pulling device for the support material, which is requiredwith known methods, can be eliminated.

A great advantage of the invention is that the adhesive which, in mostcases, is applied onto the support material before the coatingoperation, can be eliminated in almost all applicable cases. On theother hand, the invention does not exclude the use of an adhesive. Forexample, it is advisable to provide the support material with adhesivewhen the inventive sheet is used as a base material for making cylinderhead gaskets which stand freely in water.

At any rate, i.e., whether an adhesive is applied onto the supportmaterial or not, a dryer for the adhesive is eliminated in the inventivemethod (but is required in the known method disclosed in DE-AS No. 21 46309). This means a considerable saving in energy relative to the methodin accordance with DE-AS No. 21 46 309.

In the case where an adhesive is used, it is preferred in accordancewith the invention not to dry the adhesive because it assures aparticularly good adherence of the soft material on the support materialin its tacky state.

As already indicated above, the inventive method enables a concentratedadhesion of the soft material onto the support material without causingan adherenece on the calender rollers which would render the coatingunusable. A further considerable advantage of the invention can be seenin that a single oven is used for the drying and vulcanization of theapplied soft material and that these operative steps can be performed inone single operation. With respect to the known methods, in which threeor four ovens are required, considerable savings are realized by thesubject invention with respect to purchases, required space and energyconsumption, which are required for the plant for making the products.

Further savings along the aforementioned lines can be obtained with theinventive method in that the required thickness and density, as well asthe accuracy of measurement of the applied soft material layers, areobtained without the usual successive series of calibrating rollers inthe known devices.

Finally, it should be noted that the inventive method still has theadvantage over the known state of the art in accordance with DE-AS No.21 46 309 in that no kneading process, no strand pressing and nopreparation in tablet form is required for the soft material.

Therefore, the inventive method enables one to eliminate theconsiderable cost and safety preparations as required in theaforementioned method in accordance with DE-AS No. 21 46 309 (see, inparticular, column 5, paragraph 3 of the aforementioned patent). Incontrast thereto, the inventive method requires only one singleoperating step.

Other objects and features of the present invention will become apparentfrom the following detailed description considered in connection withthe accompanying drawing, which discloses one embodiment of theinvention. It is to be understood that the drawing is to be used for thepurposes of illustration only, and not as a definition of the limits ofthe invention.

In the drawing, a schematically-illustrated side view of an installationfor making a reinforced support sheet embodying the present invention isillustrated.

Referring now in detail to the drawing, the support material 10 can be astrip of sheet metal, foil, fleece or fabric which is drawn off a supplydrum or roller (not shown). As a material for the support material onecan use metal, plastic or paper. The shape and the material of thesupport material depends upon the intended use of the sheet or plate tobe made. The feeding direction is shown by an arrow 11. The mainstations of the illustrated installation are two pairs of calenderrollers 12, 13 and 14, 15, as well as a drying and vulcanization oven16. A container 17 is associated with the pairs of calender rollers 12,13 and 14, 15 which serves to receive the flowable bulk material orgoods of the soft material and apply the same into the opening betweenthe rollers 12, 13 and 14, 15 of the given pair of calender rollers. Thesoft material which is contained in containers 17 is a substance in theform of a flowable bulk material.

The soft material should comprise (by weight) at least 80% of apowder-like, asbestos-free mineral base material, for example, a groundrock and only up to 6% binder material. The remaining component, usuallyabout 3% or a maximum of 14% is composed of an asbestos-free fibermaterial, for example, a polyamide-, cellulose- or other natural- orsynthetic fibers. A fine ground shale may be used for the base material.However, other asbestos-free, powder-like mineral materials may be used.The binder material component of the soft material, preferably (in thebase condition) a synthetic rubber-toluene-mixture, is limited to about6%.

It has been found that certain properties of the reinforced supportsheet are improved, specifically with respect to resilience,adaptability, sealing property of the soft material and a reducedtendency to adhere, where the powder-like, asbestos-free mineral basematerial comprises (by weight of the total soft material) 55% to 80%chemically and thermally untreated material and 25% to 0% chemically andthermally or merely thermally treated material. Preferably slate dust isused as the chemically and thermally untreated material, although micacan also be used. For the chemically and thermally treated material,expanded graphite is advantageously used, although expanded vermiculitecan also be used but only as the thermally treated basic material.

Expanded graphite is obtained from soft mineral natural graphite or purecarbon by embedding foreign atom groups between layer planes of thegraphite crystal grating (chemical treatment), and a subsequent thermalblasting (thermal treatment). By the thermal treatment an enlargement ofthe layer distances of the graphite crystal grating is obtained.

By designating the usable basic material as vermiculite instead ofgraphite, one deals with a geological name for a group ofwater-absorbent laminated minerals having the appearance of mica. Rawvermiculite consists of thin plates, which contain crystalline water inmicroscopic size, and which expand during any sudden temperatureexposure of 800° to 1000° C. to a multiple of the original volume, whilegiving off steam. One deals here with a thermal treatment of the rawvermiculite.

The aforementioned materials are admixed in a mixer and thereby resultin the desired flowable soft material. The manufacturing method by meansof the illustrated installation is performed as follows:

The uncoated support selected from the group consisting of fabric, metalor plastic is fed between two rollers 18, 19. Thereat, it can be coatedon the surface with an adhesive, if so desired. The adhesive is presentin a container 20 above roller 18. If a coating of the support material10 with adhesive is desirous, the adhesive is "ordered" from container20 by means of a suitable conventional supply device (not shown) and isapplied onto roller 18. From roller 18, it is then applied to thesurface of the support material 10. Subsequently, the support material10 is deflected from an initial horizontal direction into a verticaldirection by means of deflection roller 21 and is fed into the openingbetween the first pair of calender rollers 12, 13. Here, the flowablesoft material is applied from container 17 onto the surface of supportmaterial 10 which may be applied with adhesive or not. Subsequently, theone-side-coated support material is fed over a further deflection roller22 and into the already mentioned oven 16 within which a first drying ofthe applied soft material occurs. When moving through the oven 16, theone-side-coated support material 10 is supported by support rollers 23.

After leaving oven 16 and, after a two-time deflection by about 90°, theone-side-coated support material 10 is fed to a second adhesive coatingdevice, whose components are provided with the same reference numeralsas the previously-described adhesive supply device 18-20 for the sake ofsimplicity and clarity. Here, the still uncoated side of the supportmaterial 10 is provided with adhesive, if so desired. Thereafter, thesupport material 10 is again deflected by means of a deflection roller25 from the horizontal direction into a vertical direction and a coatingis applied on the other side of support material 10 (if need be with thealready applied adhesive coating) by the aforementioned second pair ofcalender rollers 14, 15 and the flowable soft material which is presentin the associated container 17.

In this context, it is important to mention that the circumferentialspeeds of the individual rollers 12, 13 or 14, 15 of each pair of thecalender rollers as indicated by arrows 26, 27 or 28, 29 are unequal intheir dimension in such a manner that a fraction is exerted on the softmaterial 34, 35.

The support material which is now coated on both sides is then fed intothe interior of oven 16 by means of further deflection rollers 30. Inthis oven, the drying of the previously-applied soft material layer and,simultaneously, the vulcanization of both of the material layers isperformed. In order to provide a sufficient time for this process, threerollers 31 are provided with a relatively large diameter which assuresthat the path travelled by the coated material in the oven iscorrespondingly long (during its second throughput).

After leaving the oven 16, the finally finished reinforced support sheetis fed over a further deflection roller 32 onto a wind-up roller 33.

The aforedescribed coating method illustrated in the drawing forproducing a support material 10 coated on both sides with a softmaterial layer 34 or 35 enables the application of different materialcompounds and/or in different thicknesses, depending on the intendedload conditions of the flat gaskets which are subsequently made fromthese sheets. Thereby, the soft material layer 34 can be made of afriction-resistant material composition on the one side of the supportmaterial 10. However, these are merely examples for a possibleindividual design of the soft material layers 34, 35 and the inventionis by no means limited to such examples.

Such a design of the reinforced support sheet or plate affords anexcellent pressure resistance, good spring back resiliency, temperatureresistance and a high longitudinal and transverse stability. Therefore,high requirements can be exerted onto the products which are made bysuch a sheet or plate, for example, flat gaskets, with respect tomechanical and thermal stress. The inventive sheet or plate, as well asthe end products made therefrom are characterized by an extreme lowthickness. Because of the solid adherence of the soft material on thesupport material, no mechanical mountings are required, so that thesupport material can be smooth-faced.

Accordingly, while only one embodiment of the present invention has beenshown and described, it is obvious that many changes and modificationsmay be made thereunto without departing from the spirit and scope of theinvention.

What is claimed is:
 1. A reinforced support sheet for use in making flatgaskets comprising:a sheet-like, smooth support material; and a layer ofvulcanizable soft material covering each of the sides of said sheet-likesupport material, said soft material layers being comprised of 80% byweight of an asbestos-free, mineral base material in powder form, andalso including up to a maximum of 14% by weight of abestos-freefiber-like base material, and about 6% by weight of synthetic rubberbinder material.
 2. The reinforced support sheet as defined in claim 1,wherein said powder-like mineral base material is ground rock.
 3. Thereinforced support sheet as defined in claim 1, wherein saidasbestos-free mineral base material is in fiber form.
 4. The supportsheet of claim 3, wherein said mineral base material is comprised of 55%to 80% by total weight of said soft material of chemically and thermallyuntreated material and up to 25% to 0% of chemically and thermallytreated material.
 5. The support sheet of claim 4, wherein saidchemically and thermally untreated material is mica.
 6. The supportsheet of claim 3, wherein said mineral base material is comprised of 55%to 80% by total weight of said soft material of chemically and thermallyuntreated material and up to 25% to 0% of chemically treated material.7. The support sheet of claim 6, wherein said chemically treatedmaterial is expanded graphite.
 8. The support sheet of claim 3, whereinsaid mineral base material is comprised of 55% to 80% by total weight ofsaid soft material of chemically and thermally untreated material and upto 25% to 0% of thermally treated material.
 9. The support sheet ofclaim 8, wherein said thermally treated material is expandedvermiculite.
 10. The support sheet of claim 1, wherein said layers ofsoft material are composed of different material compounds and havedifferent thicknesses, so as to permit adjustment thereof to prevailingload conditions and wherein said soft material layers comprise afriction-resistant material.
 11. The support sheet of claim 1, whereinsaid sheet-like, smooth support material is a member selected from thegroup consisting of fabric, metal, or plastic foil.